1. Field of the Invention
The present invention relates to an operating apparatus of an engine in a portable working machine such as a blower, a bush cutter or the like.
2. Description of the Related Art
The portable working machine, for example, the blower is structured so as to spray a strong air flow to fallen leaves, dust or the like so as to collect them, and clean up. As shown in FIG. 1, the structure is made such that a worker carries an engine 8 and an air blower 11 on his or her shoulder so as to carry on the work while moving around. An injection pipe 12 is connected to a lead-out pipe 11A of the air blower 11 via a flexible pipe 13. A control handle 14 is provided in the injection pipe 12, and the worker controls the injection pipe 12 while gripping the control handle 14 (refer, for example, to Japanese Unexamined Patent Publication No. 2002-303,148 (Publication 1)). The control handle 14 is normally provided with a throttle lever for operating a throttle valve of the engine 8, and a stop switch for electrically stopping the engine.
On the other hand, in Japanese Unexamined Patent Publication No. 2001-159,320 (Publication 2) and Japanese Utility Model Publication No. 57-52,341 (Publication 3), a technique is disclosed which relates to a throttle lever and an engine stop switch used in a control handle of a portable working machine. The technique is structured such that the control handle is provided with the throttle lever which operates a throttle valve of an engine of the portable working machine by remote control via a wire, a rotating speed of the engine is increased by rotating the throttle lever in one direction so as to increase a supply amount of an air-fuel mixture, and the rotating speed of the engine is reduced by rotating the throttle lever in the other direction so as to reduce the supply amount of the air-fuel mixture. The throttle lever has a stop switch built-in for electrically stopping the engine, and the stop switch is operated at a time of operating the throttle lever in a direction of reducing the rotating speed of the engine, thereby stopping the engine.
In Japanese Patent No. 3,237,997 (Publication 4), a technique is disclosed in which a control handle of a portable working machine is provided with a throttle lever, a throttle latch for regulating an operation of the throttle lever, and a throttle lock release lever for operating the throttle latch, a rotating speed of an engine of the portable working machine is increased and reduced by the throttle lever, and the throttle lever is held by the throttle latch at a predetermined position. The throttle lock release lever cancels the hold of the throttle lever by the throttle latch. Further, the control handle is provided with an engine stop switch operated by the throttle latch. The stop switch is operated in an engine stoppable state during which the throttle lever is held by the throttle latch, and is operated in an engine operable state during which the hold of the throttle lever by the throttle latch is released by the throttle rock release lever.
In this case, the work of the blower shown in FIG. 1 is executed as follows. First, the engine 8 is started, and the injection pipe 12 is directed to a working position while operating the throttle lever. The rotating speed of the engine 8 is increased and reduced by operating the throttle lever so as to be adjusted to an airflow amount in correspondence to the working state. Further, after finishing the work, the throttle lever is returned so as to set the engine 8 in an idling state, and then the engine stop switch is operated so as to stop the engine 8.
However, when the engine stop switch is operated, the engine 8 does not generally stop immediately, and rotates a little by an inertia force in the air blower 11 or the like. At this time, since the throttle valve is at an opening degree of an idling, the air-fuel mixture is sucked into a cylinder of the engine 8.
Further, a temperature of the engine 8 is increased during the work, and it is quite usual that the temperature is not reduced so much even at a time of operating the engine stop switch. Accordingly, the air-fuel mixture is sucked into the high-temperature cylinder, and is compressed by the rotation of the engine, so that the temperature of the air-fuel mixture is increased. Therefore, when the air-fuel mixture that is sucked into the cylinder reaches a certain air-fuel ratio and temperature, the air-fuel mixture is naturally ignited, and the rotation of the engine 8 is maintained (a Run-on phenomenon). On the other hand, in a working machine having a small rotational inertia force such as a bush cutter, unlike the blower, there is a case that a self ignition is not maintained, a rapid combustion is executed within a muffler, and a noise is generated (an after burn phenomenon).
In recent years, as an exhaust gas countermeasure, an engine executing the combustion on the basis of a lean air-fuel mixture is used for improving a specific fuel consumption or the like, and the temperature of the cylinder becomes higher. Therefore, a possibility that the Run-on phenomenon or the like is generated becomes higher.
As a method of preventing the Run-on phenomenon as mentioned above, there can be considered a method of completely closing the throttle valve at a time of operating the engine stop switch so as to completely shut off the suction of the air-fuel mixture.
The techniques disclosed in Publication 2 and 3 mentioned above are structured such that the engine stop switch is turned off at the same time of operating the throttle lever in the throttle valve closing direction. Accordingly, it is possible to turn off the stop switch in a state in which the suction of the air-fuel mixture is shut off by completely closing the throttle valve, and it is possible to prevent the Run-on phenomenon or the like.
However in this structure, since the rotational resistance is applied to the throttle lever by the spring and the throttle lever is held at a certain position by the resistance where a hand is released, an operating feeling is heavy. Further, since the throttle lever is held at an optimum operation position for the work on the basis of the resistance, once the throttle lever is moved from the position, it is necessary to readjust the throttle lever by the worker for again returning to the same position. Accordingly, the techniques disclosed in Publication 2 and 3 are deteriorated in the operability of the throttle lever.
On the other hand, the technique disclosed in Publication 4 can not prevent the Run-on phenomenon as mentioned above. In other words, since the throttle lever is held at the idling operation position by the throttle latch even if the throttle lock release lever is operated so as to stop the engine, there is a possibility that the air-fuel mixture is sucked into the cylinder of the engine. Further, the throttle latch only holds the throttle lever during the engine stop, and is not applied to the throttle lever during the engine operation. Accordingly, it is necessary to always grip the throttle lever so as to operate during the work.